This invention relates to a fuel injection pumping apparatus of the kind comprising a rotary distributor member located in a housing and arranged in use to be driven in timed relationship with an associated engine, outlet ports in the housing for connection in use to the injection nozzles respectively of the associated engine, a pair of pumping plungers slidable within respective communicating radial bores in the distributor member, a delivery passage communicating with said bores and arranged to register in turn with said outlet ports during successive inward movements of the plungers, means for supplying fuel to said bores and annular cam means for imparting inward movement to the plungers.
In the case where the above type of pump is utilized to supply fuel to an engine having an even number of cylinders and therefore injection nozzles, the bores can be formed by a single drilling extending diametrically through the distributor member. The annular cam means in this case comprises an annular cam ring having a plurality of pairs of inwardly directed cam lobes on its internal surface, the number of pairs of cam lobes being equal to half the number of engine cylinders. Each plunger is moved inwardly at substantially the same time so that the loads on the distributor member are substantially balanced.
In order to supply fuel to an engine having an odd number of cylinders it is possible for say a three cylinder engine, to provide three plungers together with the associated bores, the three bores having their axes displaced by 120.degree. about the axis of rotation of the distributor member. The annular cam ring is provided with three equi-angularly spaced lobes and again the loads acting on the distributor member are substantially balanced. A disadvantage of this arrangement is that the production of the bores in the distributor member is difficult and expensive. It is known to supply fuel to a three cylinder engine using an apparatus designed to supply fuel to a six cylinder engine and to connect alternate outlets to a drain. This solution is not however an ideal solution since half the quantity of fuel which is delivered by the apparatus flows to a drain and this is wasteful of energy as well as causing unnecessary heating of the fuel. This latter solution is not practical for an apparatus intended to supply fuel to a five cylinder engine because it would mean that the apparatus would have to be designed to supply fuel to a ten cylinder engine.